Biological materials

ABSTRACT

The followings are disclosed herein: 
     a biomaterial comprising calcium phosphate and a copolymer of lactic acid, glycolic acid and ε-caprolactone; 
     a biomaterial for the induction of osteoanagenesis, characterized in that a periosteum is attached to the biomaterial comprising calcium phosphate and a copolymer of lactic acid, glycolic acid and ε-caprolactone; and a biomaterial for the prevention of adhesion comprising calcium phosphate and a copolymer of lactic acid, glycolic acid and ε-caprolactone where the molar ratio of lactic acid, glycolic acid and ε-caprolactone is within a range of 5-90:3-75:5-40.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a biomaterial comprising calciumphosphate and a copolymer of lactic acid, glycolic acid andε-caprolactone and, more particularly, it relates to an excellentmaterial for organism which is applied to reconstruction of hard tissuesand soft tissues in vivo and is gradually degraded and absorbed togetherwith the tissue formation. The present invention further relates to abiomaterial for the induction of osteoanagenesis where periosteum isprovided to the above biomaterial by means of suture or adhesion and,particularly, to a biomaterial for the induction of osteoanagenesiswhich is applied as a quick therapy of big bone defect and is graduallydegraded and absorbed. The present invention furthermore relates to abiomaterial for the prevention of adhesion which is applied for theprevention of adhesion of the tissues produced as a result of aself-repair after an operation or by damage of tissues of organism andis gradually degraded and absorbed.

2. Description of the Related Art

Defected area in organism which is caused by injury, inflammation, tumorexcision or reconstructive cosmetology of hard tissues such as bonetissue and cartilaginous tissue and soft tissues such as epithelialtissue, connective tissue and nervous tissue has already been subjectedto a prosthetic treatment and to a functional recovery by variousmethods and there have been also many studies for the materials usedtherefor.

In subjecting the bone defect area in organism to a prosthetictreatment, a self bone implantation showing abetter take to implantedarea and having less infection of virus, prion, etc. or lessimmunological problem than homoimplantation and heteroimplantation hasbeen carried out already. However, in the case of the self boneimplantation, there is a limitation in a collectable amount and, inaddition, there are problems such as a risk for infection by formationof new surgical wound for obtaining the bone to be implanted and atendency that pain of the patient becomes longer.

As a substitute for a self bone implantation, there is a method wheremetal materials such as stainless steel and titanium alloy are used asartificial biomaterials and, because of a significant progress ofbiomaterials and an easy availability of the materials, they have beenused actually.

However, in those biomaterials, their physical and mechanical strengthis much more than that of tissues of organism and there is a toxicity ofthe metal contained therein due to corrosion. In addition, theiraffinity to organism is inferior as well.

Therefore, as a method for improving the affinity to organism, there hasbeen conducted a method where the surface of the metal material issubjected to a surface treatment by a bioaffinitive material such ashydroxyapatite whereby its affinity to the surrounding tissues isimproved but that is still insufficient.

On the other hand, as bioaffinitive materials, polymers of lactic acid,glycolic acid, trimethylene carbonate or lactone such as ε-caprolactoneand copolymers thereof which are biodegradable aliphatic polyesters havebeen investigated as reparative materials as well and, in addition, ablock copolymer of polylactic acid, poly-ε-caprolactone and polyglycolicacid as mentioned in Japanese Patent Laid-Open Hei-09/132638 has alsobeen investigated. However, those materials lower their mechanicalstrength upon degradation in vivo resulting in a fatigue deteriorationand, although bone conduction is not inhibited, they rarely show anaction for bone induction.

On the other hand, bioceramics such as alumina, bioglass, A-Wcrystallized glass and hydroxyapatite have a high bioaffinity, have beenutilized as materials for artificial bone, dental implant, etc. andnoted of formation of new bone on the surface in organism and haveexcellent filling function and adhesion to bone tissues.

However, since those are the materials which are not absorbed inorganism, there is a problem that they remain in the formed bone tissuesand affect the growth of new bones and that strength of the bone lowers.Tricalcium phosphate is a material which is absorbed in vivo and, whenit is used to a defected area of bone, it is absorbed or collapsed fromthe surface of the material and is substituted for the new bone, but itsmechanical strength is weak as compared with the bone, its use to thearea where load such as body weight is applied is limited.

In addition, tricalcium phosphate is in granules and, therefore, it haslittle ability of giving a shape to a bone implantation material and ofmaintaining/stabilizing thereof whereupon there is a problem that afilling operation is difficult to a complicated and broad defect andthat cure is delayed due to flowing-out of the granules.

In order to solve such problems, many materials where bioceramics andpolymers are compounded have been studied. In U.S. Pat. No. 4,347,234, acomplex of bioceramics with collagen is proposed. However, when suchcollagen i s used, its molecular weight, amino acid composition,quantity, water-holding amount, etc. are not constant because it is amaterial derived from nature and, in addition, a complete removal of itcauses a foreign body reaction in vivo and foreign body giant cell andother phagocytes, etc. are activated whereupon a bone induction ishardly expressed.

In place of collagen, there have been proposals for many materials wherealiphatic polyesters such as polylactic acid having no problem in termsof immunology are compounded with hydroxyapatite. In Japanese PatentLaid-Open Hei-10/324641, there is disclosed an absorbable isolatingmembrane consisting of calcium phosphate and a lactic acid typepolyester having a dicarboxylic acid and a diol where a polymerizationcatalyst is inactivated. In U.S. Pat. No. 4,595,713, there is discloseda complex consisting of a osteoanagenetic substance such as calciumβ-phosphate and hydroxyapatite and a copolymer of lactic acid withε-caprolactone where ε-caprolactone occupies the most of the amount. Theformer is absorbable in vivo and has a bone induction property but,since a lactic acid segment and other components are blocked, propertyof calcium phosphate appears and properties of forming, retaining andstabilizing the shape are little. In the latter, its mechanical strengthto the applied tissue is low and a degradation rate of the material isslow whereby osteoanagenesis is suppressed. In any of the materials, theproblem of little osteoanagenetic amount of calcium β-phosphate in vivois not solved.

In Japanese Patent Laid-Open Hei-06/298639, there is disclosed asustained-released material where tricalcium β-phosphate is dispersed ina complex of an antibiotic substance with a lactic acid/glycolic acidcopolymer.

Although there have been many other studies concerning reconstruction ofsoft tissues such as blood vessel and peripheral nerve, a sufficientmaterial has not been available and, accordingly, there has been ademand for a material having a metabolism similar to that of tissueswhere a biocompatibility is excellent, strength can be maintained untilthe tissues are regenerated and degradation and absorption take placeafter the implantation.

With regard to a biomaterial for induction of osteoanagenesis, a soleuse of a material has a limitation for the therapeutic effect and,therefore, with an object of supplementing the osteoanagenetic amount,there have been many studies for a substitution therapy where filling ofbone marrow is utilized. Since bone marrow has many osteoanageneticcells, its bone inducing property is high. However, with regard to theuse of bone marrow, there is a limitation in the collecting amountthereof. In addition, its application is complicated and, to a defect ina broad area, a filling operation is difficult and there has been nosatisfactory material in terms of a shape-giving property and aretention-stabilizing property. for the prevention of flowing out.

On the other hand, with regard to a material having an osteoanageneticability like bone marrow, there is a periosteum where osteoblasts areabundantly present. As compared with bone marrow, periosteum can beeasily collected in large quantities as a membrane without leaving asurgical wound and there is no invasion in the bone wherefrom it iscollected because it is regenerated even if taken out. In addition,periosteum is a tough membrane and, therefore, there is no problem suchas flowing-out at bone marrow.

As such, it has been expected to conduct a treatment of a big bonedefect area by application of periosteum and a material having anosteoanagenetic property but it is a current status that noosteoanagenetic material having a sufficient property for retaining andstabilizing the periosteum in a filmy form has been available.

Now, biomaterials for the prevention of adhesion will be discussed. Atissue adhesion which is a physiological action after orthopedic,cerebral, thoracic and abdominal surgical operations is due to anadhesion of the organs with the surrounding tissues caused by theproduction of collagen fiber by fibroblasts as a result of damage of thetissue. Generation of complications accompanied by such an adhesion oradhesion of the nerve with the area where scarred tissue is formedcauses pain, biofunction disturbance, etc. and, therefore, that is aproblem to a patient due to psychic and physical pain.

With regard t o such a problem, various methods and many materials usedtherefor have been studied already. For example, prevention of theadhesion by means of administration of a pharmacological agent such asantithrombotic agent or application of a hyaluronic acid solution or acopolymer of ethylene oxide and propylene oxide is available but,although such a method has a temporary adhesion-preventing action, thereis a disadvantage that it is apt to flow out and does not have asustained effect.

For a physical separation of biotissues, there has been carried out amethod where silicon, Teflon, polyurethane, oxidized cellulose, or thelike is used as a film for the prevention of adhesion. However, they arenon-absorbable materials and, therefore, they remain on the surface ofthe biotissues, which results in not only a delay in repair of thetissues but also a cause of infection and inflammation.

As a means for solving such a problem, Japanese Patent Laid-OpenHei-03/295561 proposes a film where collagen is a main component. Inaddition, cattle pericardium and horse pericardium which arecross-linked with glutaraldehyde are available. However, when such acollagen is used, a complete removal of a telopeptide moiety havingantigenicity is difficult and there is a risk of contamination of prionor the like since collagen is a material derived from nature. Further,an aldehyde or an isocyanate is used as a cross-linking agent forcontrolling the degradation of the adhesion-preventing film but, in theuse of such an agent, the degraded product shows a bad affection in vivoand that is not preferred.

In Japanese Patent Laid-Open Sho-60/14861, in place of collagen, thereis proposed an adhesion-preventing material consisting of abiodegradable/bioabsorbable high-molecular material such as a copolymerof lactic acid with glycolic acid or a copolymer of lactic acid withcaprolactone having no problem in terms of immunology. In JapanesePatent Laid-Open Hei-11/192299, there is disclosed a complex materialconsisting of a biologically active ceramics and a copolymer comprisinga combination of p-dioxanone, lactic acid, trimethylene carbonate andcaprolactone.

When the inside of the organism changes to a circumstance where adhesionof tissue takes place, tissues become very adhesive to each other and,therefore, a mechanical strength is required because it is necessary tokeep the effect of preventing the adhesion for 1-2.5 months and theadhesion-preventing material is held to the tissue by means of suture.However, those materials are insufficient in terms of both degradationand strength retention.

Although there have been many studies for the prevention of adhesion oftissues as such, no material having a sufficient property as a materialfor the prevention of adhesion has been available and it is the currentstatus that there has been a demand for a soft material which has anexcellent biocompatibility, does not cause an immune reaction such asflare, swelling and induration at the site where the adhesion-preventingmaterial is applied, prevents the adhesion during the period until thetissues are repaired and is degraded and absorbed within a short periodafter the tissues are repaired.

In order to solve the above-mentioned problems, the present inventorshave carried out an intensive study for a biomaterial which has abiodegradability, does not produce a foreign body reaction in vivo, hasappropriate strength and degradability and is effective for theregeneration of tissues.

The present inventors have further carried out an intensive study for abiomaterial having an appropriate softness for retention andstabilization of periosteum as an osteoanagenesis inducing material andalso for a biomaterial for induction of osteoanagenesis produced byattaching periosteum thereto.

The present inventors have furthermore carried out an intensive studyfor a biomaterial for the prevention of adhesion which has abiodegradability, does not produce a foreign body reaction in vivo, hasappropriate strength and degradability and does not inhibit the repairof the tissues as an adhesion-preventing material.

As a result, the present invention which will be mentioned in detail ashereunder has been accomplished.

SUMMARY OF THE INVENTION

Thus the present invention relates to a biomaterial comprising calciumphosphate and a copolymer of lactic acid, glycolic acid andε-caprolactone.

The present invention further relates to a biomaterial for the inductionof osteoanagenesis where periosteum is attached by means of suture oradhesion to a biomaterial comprising calcium phosphate and a copolymerof lactic acid, glycolic acid and ε-caprolactone where the molar ratioof lactic acid, glycolic acid and ε-caprolactone is within a range of5-90:3-75:5-40 molar %.

The present invention still further relates to a biomaterial for theprevention of adhesion comprising calcium phosphate and a copolymer oflactic acid, glycolic acid and ε-caprolactone where the molar ratio oflactic acid, glycolic acid and ε-caprolactone is within a range of5-90:3-75:5-40 molar %.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now the present invention will be illustrated in more detail ashereinafter.

The copolymer of lactic acid, glycolic acid and ε-caprolactone used inthe present invention may be that which is prepared by any method so faras it is manufactured by common means. An example for the manufacture isthat lactide, glycolide and ε-caprolactone are heated in the presence ofa catalyst such as stannous octoate, tin chloride, dibutyl tindilaurate, aluminum isopropoxide, titanium tetraisopropoxide andtriethyl zinc to carry out a ring-opening polymerization at 100° C. to250° C. Monomer of the lactic acid and the lactide used for thepolymerization may be any of D-, L- and DL-compounds or may be a mixturethereof. When monomer and oligomer are present in the resultingcopolymer, tissue reaction and degradation rate are abnormallyaccelerated and degraded segments are produced in theabsorbing/degrading ability more than that of macrophage, whereby thetissue degeneration is caused. Accordingly, it is preferred to use afterbeing purified by, for example, means of reprecipitation.

The copolymer of lactic acid, glycolic acid and ε-caprolactone varies inits mechanical strength, softness and hydrolyzing rate depending uponthe composition and the molecular weight and, with regard to thecopolymer used in the present invention, it is preferred that theε-caprolactone content therein is 1-45 molar %. When the content ofε-caprolactone is less than 1 molar %, the copolymer has a high rigidityand is fragile and, therefore, it cannot be applied because the closeadhesion to the biotissues lowers and the degradation rate becomes slow.On the contrary, when the content is more than 45 molar %, the necessarystrength is not achieved and, in addition, the biodegradability andbloabsorbability become slow and that is not preferred.

The lactic acid content and the glycol acid content in the copolymer canbe freely changed but, when the glycolic acid content is less than 5molar %, there are problems that the necessary degradation rate is notachieved and that regeneration of the tissues is inhibited while, whenit is more than 70 molar %, tissue degeneration may be resulted due tothe above-mentioned degraded segments.

The biomaterial of the present invention is in such a structure thatcalcium phosphate is coordinated by a carbonyl group of the copolymer oflactic acid, glycolic acid and ε-caprolactone and, therefore,biodegradability and biotissue inducing ability of calcium phosphate areadjusted whereby its biotissue inducing ability can be significantlypromoted. Generally, the shape of the reconstructed biotissue iscomplicated but, when the composition and the molecular weight of thecopolymer of lactic acid/glycolic acid/ε-caprolactone are adjusted,various types of material ranging from flexible ones to highly strongones are formed and, accordingly, the biomaterial of the presentinvention is not deformed by compression of the tissue but is able to befixed in a tightly closed manner to the tissue. In addition, it ispossible to adjust to the degradation rate which is adaptable to thewound of the site to be applied and, therefore, regeneration of thebiotissue is not inhibited but a quick tissue repair is possible.

Thus, when the biomaterial of the present invention is used as areconstructing material for hard and soft tissues in vivo, it is quicklyand directly bonded to the tissue, retains its strength during theperiod until the tissue is regenerated and is gradually absorbed intothe organism together with the formation of the new biotissue and,accordingly, it is a biocompatible material which is able to be appliedto a broad area.

As hereunder, the biomaterial for the induction of osteoanagenesisaccording to the present invention will be mentioned in detail.

With regard to the periosteum used in the present invention, aself-periosteum is preferred and, in the case of such a self-periosteum,it is possible to use after collecting from all sites of the organismwherefrom periosteum can be collected. For example, when the periosteumexcised by a primary surgical operation in the therapy of bone defectsite is used, it is easily available in large quantities. The periosteumwhich is collected before the operation and is preserved can be used aswell. The above-mentioned periosteum is that which is derived fromorganism but, if an artificial periosteum having the substantially samefunction as the above-mentioned periosteum derived from organism will bedeveloped in future, such an artificial periosteum may be used as well.

Attachment of the periosteum to the biomaterial may be carried out byany means so far as the periosteum can be fixed and its examples are asuture by means of an absorbable suture and an adhesion by means of afibrin adhesive. The form of the attachment of the periosteum to thebiomaterial may be freely designed depending upon the form (fiber, film,block, tube, etc.) of the biomaterial. For example, the periosteum maybe attached to all of or a part of the surface (one side, both sides,inner surface or outer surface) of the biomaterial depending upon theobject of the therapy.

The preferred form of the osteoanagenesis inducing material according tothe present invention is a filmy shape where periosteum is attached bythe above-mentioned means to the surface of the biomaterial in a filmyform and is made round into a tubular form so that the periosteum iscontacted to the bone defect site.

It is preferred that the rigidity of the osteoanagenesis inducingmaterial of the present invention is adjusted to 200-20000 MPa at 4-40°C. When it is less than 200 MPa, the rigidity is low and is too soft toapply to the filmy shape while, when it is more than 20000 MPa, therigidity is high and is too hard to apply to the filmy shape whereby itis impossible to attach the periosteum to the defect site.

Method for the manufacture of the copolymer of lactic acid, glycolicacid and ε-caprolactone used in the present invention is as mentionedalready.

With regard to the copolymer which is used as the material for theinduction of osteoanagenesis of the present invention, a copolymer oflactic acid, glycolic acid and ε-caprolactone where the molar ratio oflactic acid, glycolic acid and ε-caprolactone is within a range of5-90:3-75:5-40 molar % preferred.

Here, when the content of ε-caprolactone is less than 5 molar %, thecopolymer has a high rigidity and is fragile whereby attachment of theperiosteum thereto is difficult and there is possibility that thebiotissue is damaged by the polymer segments. On the other hand, when itis more than 40 molar %, the necessary strength is not achieved and, inaddition, biodegradability and bioabsorbability become slow.

The contents of lactic acid and glycolic acid in the copolymer can befreely changed but, when the glycolic acid content is less than 3 molar%, there are problems that the necessary degradation rate is notachieved and that the tissue repair is disturbed while, when it is morethan 75%, damage of the tissue may take place by the degraded segmentsmentioned above.

The lactic acid content in the copolymer is within a range of 5-90 molar% and, when the lactic acid content is less than 5 molar %, thenecessary degradation rate is not achieved and repair of the bone tissueis inhibited while, when it is more than 90 molar %, the rigiditybecomes high and there is, a possibility that the biotissue is damagedby the polymer segments.

Now, the biomaterial for the prevention of adhesion according to thepresent invention will be mentioned in detail.

Method for the manufacture of a copolymer of lactic acid, glycolic acidand ε-caprolactone used in the present invention is as mentioned above.

With regard to the copolymer which is used for the present invention, acopolymer of lactic acid, glycolic acid and ε-caprolactone where themolar ratio of lactic acid, glycolic acid and ε-caprolactone is within arange of 5-90:3-75:5-40 molar % is preferred.

Here, when the content of ε-caprolactone is less than 5 molar %, thecopolymer has a high rigidity and is fragile whereby there is apossibility that the biotissue is damaged by the polymer segments. Onthe other hand, when it is more than 40 molar %, the necessary strengthis not achieved and, in addition, biodegradability and bioabsorbabilitybecome slow.

The contents of lactic acid and glycolic acid in the copolymer can befreely changed but, when the glycolic acid content is less than 3 molar%, there are problems that the necessary degradation rate is notachieved and that the tissue repair is inhibited while, when it is morethan 75%, damage of the tissue may take place by the degraded segmentsmentioned above.

The lactic acid content in the copolymer is within a range of 5-90 molar% and, when the lactic acid content is less than 5 molar %, thenecessary degradation rate is not achieved and repair of the bone tissueis inhibited.

When it is more than 90 molar %, the rigidity becomes high and there isa risk that the biotissue is damaged by the polymer segments.

It is preferred that the number-average molecular weight of thecopolymer of lactic acid, glycolic acid and ε-caprolactone is30,000-200,000. When the molecular weight of the copolymer is out of theabove range and is lower than 30,000, a lot of monomers and oligomerssuch as lactic acid and glycolic acid are contained and, therefore,there is a problem of strong stimulation to the biotissues and, inaddition, hydrolysis is promoted resulting in a reduction in thestrength whereby physical properties and adhesion-preventing effectduring the necessary period are not available. On the other hand, whenthe molecular weight is more than 200,000, the hydrolyzing rate lowersinhibiting the repair of bone tissues and, in addition, a mixingoperation with calcium phosphate is difficult whereby dispersion ofcalcium phosphate in the copolymer becomes non-homogeneous.

Incidentally, other copolymer components in small quantities may becontained as well within such an extent that the object of the presentinvention is not deteriorated. Examples of such copolymer components areβ-hydroxybutyric acid and a cyclic monomer constituting ahydroxycarboxylic acid such as γ-butyrolactone and δ-valerolactone.

Examples of the calcium phosphate used in the present invention aretricalcium phosphate, hydroxyapatite and calcium secondary phosphate.The most preferred calcium phosphate in relation to the copolymer of thepresent invention is tricalcium phosphate which has a good affinity tothe copolymer and is substituted with new tissues by absorption anddisintegration in vivo promoting the regeneration and the repair of bonetissues. It is preferred to use calcium phosphate having an averageparticle size of 0.1 to 200 μm. When the average particle size is lessthan 0.1 μm, the dissolving rate is too quick to show a sufficienttissue-reconstructing ability and, in addition, degradation of thematerial is promoted whereby sufficient effects of bone repair andadhesion prevention are not achieved. On the contrary, when the averageparticle size is more than 200 μm, the dissolving rate becomes slowwhereby the tissue reconstruction is inhibited and, in addition, thetissue repair is delayed due to calcium phosphate existing on thesurface of the material. Further, the preferred tricalcium phosphate inthe present invention is tricalcium phosphate which is sintered at650-1500° C. As a result of the sintering, structure of tricalciumphosphate is stabilized resulting in a high density and, when thesintering temperature is lower than 650° C., an unstable structure wherehydrated water is present in tricalcium phosphate is resulted wherebydegradation of the polymer is promoted upon compounding. On thecontrary, when it is higher than 1500° C., tricalcium phosphate beginsto decompose and the components which inhibit biotissue reconstruction,bone tissue repair and biotissue repair are produced.

In order to prepare a biomaterial which has appropriate strength anddegradation property and which is effective for the tissue regeneration,an osteoanagenetic induction material which is effective for the bonetissue repair and a material for the prevention of adhesion in thepresent invention, it is necessary to prepare a biomaterial, that is acomplex of calcium phosphate with a copolymer of lactic acid, glycolicacid and ε-caprolactone. Such a complex or a biomaterial can bemanufactured, for example, by the following method.

Thus, it is manufactured by heating and kneading calcium phosphate witha copolymer of lactic acid, glycolic acid and ε-caprolactone at thetemperature of higher than the softening point of the copolymer.Although the condition of heating and kneading cannot be specifiedbecause it varies depending upon, for example, the composition and themolecular weight of the copolymer of lactic acid, glycolic acid andε-caprolactone used and also upon the type and the physical property ofcalcium phosphate, it is preferably carried out in vacuo, in air or in anitrogen atmosphere at 50-250° C. With regard to the kneading time,about 5-60 minutes are required. Examples of the methods for themanufacture of the biomaterial other than the heating/kneading methodare a method where calcium phosphate is mixed with a copolymer of lacticacid, glycolic acid and ε-caprolactone in a solvent followed by removingthe solvent and a method where they are subjected to a solid mixingfollowed by being subjected to a pressurized press or to a heatingpress.

Calcium phosphate and a copolymer of lactic acid, glycolic acid andε-caprolactone may be mixed in any ratio and the resulting complexvaries in its physical property such as tensile strength and degradationrate depending upon the mixing ratio. In general, however, it ispreferred that the mixing ratio of calcium phosphate to the copolymer oflactic acid, glycolic acid and ε-caprolactone in terms of weight is1:0.1˜2.0. When the content of the copolymer of lactic acid, glycolicacid and ε-caprolactone is less than 0.1, the complex becomes fragileand lowers its shape-giving property and retention stability while, whenthe content of the copolymer of lactic acid, glycolic acid andε-caprolactone is more than 2.0, the necessary strength and rigidity arenot achieved and the tissue inducing and regenerating ability and thefunctions as an osteoanagenesis inducing material and an adhesionpreventing material are reduced.

It is also possible that pharmaceuticals such as physiologicalsubstances including anti-tumor agent, anti-cancer agent,anti-inflammatory agent, vitamins (for example, vitamin D of anactivated type) and polypeptide (for example, a thyroid stimulatinghormone) are added to the complex to give a sustained released functionwhereby the tissue regeneration and the bone tissue repair are promotedwithin such an extent that the characteristics of the biomaterial,osteoanagenetic inducing material and adhesion preventing materialobtained by the present invention are not deteriorated. It is furtherpossible that the biomaterial, the osteoanagenesis inducing material andthe adhesion preventing material of the present invention are used as anadhesion preventing film, an artificial blood vessel, a nerve repairinducing pipe, etc.

The complex and the osteoanagenesis inducing material which aremanufactured as such can be molded by known methods such as casting,injection molding, extrusion molding and hot press and may be used inany form such as fiber, film, block and tube. It is also possible toprepare a porous product by, for example, means of a freeze-drying froma solvent.

In addition, the biomaterial, the osteoanagenesis inducing material andthe adhesion preventing material according to the present invention havecharacteristics that they can be easily deformed by heating by, forexample, means of dipping in hot water whereby their filling into acomplicated site to be treated can be carried out easily. During theperiod from embedding and filling into organism until regeneration andrepair of the tissue, the complex and the biomaterial retain their formand strength even near the body temperature and are quite effective forthe utilization even to the site where a load such as body weight isapplied.

EXAMPLES

The present invention will be further illustrated by way of thefollowing examples although the present invention is not limitedthereto. Incidentally, % stands for that by weight in all cases unlessotherwise mentioned.

Example 1

L-Lactide (220 g), 35 g of glycolide and 45 g of ε-caprolactone weresubjected to a polymerization reaction in the presence of 0.01 g ofstannous octoate in vacuo (10⁻³ mmHg) at 150° C. for 24 hours. After thereaction, the product was purified by dissolving in chloroform followedby separating in methanol to give 185g of copolymer of lactic acid,glycolic acid and ε-caprolactone.

The number-average molecular weight of the copolymer prepared as such bymeans of a GPC was 120,000 and its composition by means of an H-NMR interms of molar ratio of lactic acid, glycolic acid and ε-caprolactonewas 80:15:5.

The above-prepared copolymer of lactic acid, glycolic acid andε-caprolactone was heated and kneaded at 200° C. for 10 minutes withtricalcium β-phosphate of an average particle size of 1 μm sintered at800° C. in a ratio of 30/70 by weight. According to the result of thestrength test, the resulting complex had a uniform composition, showed astrength near the bone strength and had a bending strength of 70 MPa anda Young's modulus of 25 GPa. As a result of the cell incubationexperiment, both of tricalcium phosphate and the copolymer of lacticacid, glycolic acid and ε-caprolactone used for the complex showed thecharacteristics to organisms prior to making into a complex.

Examples 2-9

Copolymers of lactic acid, glycolic acid and ε-caprolactone havingvaried compositions were synthesized and made into complexes by mixingwith calcium phosphate having different physical property in the ratiosas shown in Tables 1-2 whereupon biomaterials were manufactured. Theresults are shown in Tables 1-2. Incidentally, their number-averagemolecular weights were about 90,000-120,000.

TABLE 1 Tricalcium β- Composition of Complex Property CompositionPhosphate (Ratio by Weight) of Biomaterial of Copolymer Average SinteredTricalcium Bending Young's (Molar Ratio) Particle Temp. β- StrengthModulus Ex LA GA CL Size (μm) (° C.) Phosphate Copolymer (MPa) (GPa) 268 18 14 1 800 70 30 55 20 3 70 25 5 1 800 50 50 40 3 4 75 20 5 1 1200 70 30 60 18 5 75 20 5 100 800 70 30 65 20 6 60 10 30 1 800 70 30 40 2Note: LA . . . L-Lactic Acid GA . . . Glycolic Acid CL . . .ε-Caprolactone

TABLE 2 Calcium Phosphate Property of Composition Species (sinteredComposition of Complex Biomaterial of Copolymer temperature: (Ratio byWeight) Bending Young's (Molar Ratio) 800° C.; average Calcium StrengthModulus Ex LA GA CL particle size: 1 μm) Phosphate Copolymer (MPa) (GPa)7 80 15 5 Tricalcium α- 70 30 40 15 Phosphate 8 75 20 5 Hydroxyapatite50 50 70 15 9 75 20 5 Hydroxyapatite 70 30 100 20

<Evaluation of Biotissue Inducing Ability>

The biomaterials manufactured in Examples 2-4 were made into a filmhaving a thickness of about 200 μm using a hot press, sterilized withethylene oxide and implanted to an artificial defect of mandible of adog. As a result, the complex film disappeared within about 4 weeks andthe defect part was reconstructed within about 12 weeks.

Comparative Example 1

A binary copolymer of lactic acid with glycolic acid (80:20) having anumber-average molecular weight of 100,000 was synthesized by the samemethod as in Example 1. This was heated and kneaded at 200° C. for 10minutes with tricalcium α-phosphate being sintered at 800° C. and havingan average particle size of 1 μm in a ratio of 70/30 by weight whereupona complex was synthesized.

The resulting complex had a high rigidity and was fragile and,accordingly, its molding was difficult or, in other words, its shape wasunable to be retained.

Comparative Example 2

A binary copolymer of lactic acid with ε-caprolactone (70:30) having anumber-molecular weight of 110,000 was synthesized in the same way as inComparative Example 1 and a complex was synthesized by the same methodas in Comparative Example 1. The complex was made into a film having athickness of about 200 μm using a hot press, sterilized with ethyleneoxide and implanted to an artificial defect of mandible of a dog. As aresult of an observation for about 12 weeks, the degradation rate of thecomplex was slow and regeneration of the tissue was inhibited.

Example 10 Evaluation of Bone Tissue Inducing Ability

L-Lactide (220 g), 35 g of glycolide and 196 g of ε-caprolactone weresubjected a polymerization reaction in the presence of 0.01 g ofstannous octoate in vacuo (10⁻³ mmHg) at 150° C. for 24 hours. After thereaction, the product was purified by dissolving in chloroform followedby separating in methanol to give 273 g of a copolymer of lactic acid,glycolic acid and ε-caprolactone.

A number-average molecular weight of the copolymer prepared as such bymeans of a GPC was 100,000 and its composition (molar ratio) by means ofan H-NMR was lactic acid/glycolic acid/ε-caprolactone=65/8/27.

The resulting copolymer of lactic acid, glycolic acid and ε-caprolactonewas heated and kneaded at 180° C. for 10 minutes with tricalciumβ-phosphate being sintered at 800° C. and having an average particlesize of 10 μm in the ratio as shown in Table 3 whereupon a complex wasprepared.

The biomaterial prepared as such was molded by a hot press method tomanufacture a film having a thickness of 200 μm followed by sterilizingwith ethylene oxide. Result of the physical property is shown in Table3.

TABLE 3 Physical Property of Calcium β- Complex Material Composition ofPhosphate Composition of Complex (Room Temp) Copolymer Average Sintered(Ratio by Weight) Tensile Ex (Molar Ratio) Particle Temp. Calcium β-Strength Rigidity 10 LA GA CLT Size(μm) (° C.) Phosphate Copolymer (MPa)(MPa) 65 8 27 10 800 50 50 33 2300

Result of the cell incubation test was that both of the tricalciumphosphate and the copolymer of lactic acid, glycolic acid andε-caprolactone used as the above-mentioned filmy biomaterials retainedtheir characteristics to organism before making into the complex.

An evaluation was carried out using an artificially deficient animalmodel where tibia of a dog was deficient in 20 mm. Periosteum collectedfrom the defect part was sutured on the surface of the above-mentionedfilmy biomaterial to prepare a filmy osteoanagenesis inducing material,the resulting osteoanagenesis inducing material was made round in atubular shape so as to contact to the bone defect site and, at the sametime, implanted by an absorbable suture so as to cover the defect partfollowed by fixing using an external skeletal fixer and then the elapseof the osteoanagenesis was observed by means of X-ray or the like.

As a result, disappearance of the osteoanagenesis inducing materialafter 4 weeks from the implantation and an early induction ofregeneration of the bone at the defect site were observed by anobservation of X-ray picture. After 8 weeks from the implantation, theanimal was able to walk even when a wire of the external skeletal fixerwas partially cut. After 12 weeks, an incision was conducted anddisappearance of the osteoanagenesis inducing material and regenerationof the bone defect part were confirmed by naked eye. After 24 weeks, theanimal was completely able to walk in such a state that the externalskeletal fixer was removed.

Comparative Example 3

In accordance with the same method as in Example 10, a binary polymer oflactic acid and glycolic acid (80:20) having a number-average molecularweight of 100,000 was synthesized. This was heated and kneaded at 200°C. for 10 minutes with tricalcium α-phosphate being sintered at 800° C.and having an average particle size of 1 μm in a ratio of 70/30 byweight whereupon a complex was synthesized.

Since the resulting complex had a high rigidity and was fragile, itsmolding was difficult and the attaching the periosteum thereto using anabsorbable suture was impossible either.

Comparative Example 4

In accordance with the same method as in Comparative Example 3, a binarycopolymer of lactic acid and ε-caprolactone (70:30) having anumber-average molecular weight of 110,000 was synthesized and then acomplex was synthesized by the same method as in Comparative Example 3.The complex was made into a film having a thickness of about 200 μmusing a hot press and sterilized with ethylene oxide, periosteum wasattached thereto using an absorbable suture and the product wasimplanted to a bone defect part of tibia of a dog. After 12 weeks, anincision was conducted and an observation by naked eye revealed that thedegradation rate of the complex was so slow that its residue was notedwhereupon regeneration of the bone defect part was inhibited.

Example 11

L-Lactide (210 g), 35 g of glycolide and 53 g of ε-caprolactone weresubjected to a polymerization reaction in vacuo (10⁻³ mmHg) at 150° C.for 24 hours in the presence of 0.01 g of stannous octoate. After thereaction, the product was purified by dissolving in chloroform followedby separating in methanol whereupon 180 g of a copolymer of lactic acid,glycolic acid and ε-caprolactone were obtained.

The number-average molecular weight by means of a GPC of the copolymerprepared as such was 110,000 and the composition (in terms of molarratio) by means of an H-NMR was lactic acid:glycolicacid:ε-caprolactone=78:15:7.

The above-prepared copolymer of lactic acid, glycolic acid andε-caprolactone was heated and kneaded at 200° C. for 10 minutes withtricalcium β-phosphate of an average particle size of 1 μm sintered at800° C. in a ratio of 30/70 by weight. According to the result of thestrength test, the resulting complex had a uniform composition and had abending strength of 68 MPa and a Young's modulus of 25 GPa. As a resultof the cell incubation experiment, both tricalcium phosphate and thecopolymer of lactic acid, glycolic acid and ε-caprolactone used for thecomplex showed the characteristics to organisms as same as those priorto making into a complex.

Examples 12-17

Copolymers of lactic acid, glycolic acid and ε-caprolactone havingvaried compositions were synthesized and made into complexes by mixingwith calcium phosphate having different physical property in the ratiosas shown in Tables 4-5where upon adhesion preventive materials weremanufactured. The results are shown in Tables 4-5. Incidentally, thenumber-average molecular weights of the copolymers were about90,000-120,000.

TABLE 4 Tricalcium β- Composition of Complex Property CompositionPhosphate (Ratio by Weight) of Biomaterial of Copolymer Average SinteredTricalcium Bending Young's (Molar Ratio) Particle Temp. β- StrengthModulus Ex LA GA CL Size (μm) (° C.) Phosphate Copolymer (MPa) (GPa) 1235 48 17 1 800 70 30 30 3 13 75 20 5 1 1200  70 30 60 18 14 75 20 5 100800 70 30 65 20 15 62  7 31 1 800 70 30 50 5 Note: LA . . . L-LacticAcid GA . . . Glycolic Acid CL . . . ε-Caprolactone

TABLE 5 Calcium Phosphate Property of Composition Species (sinteredComposition of Complex Biomaterial of Copolymer temperature: 800° C.;(Ratio by Weight) Bending Young's (Molar Ratio) average particle CalciumStrength Modulus Ex LA GA CL size: 1 μm) Phosphate Copolymer (MPa) (GPa)16 78 15 7 Tricalcium α- 70 30 38 15 Phosphate 17 50 45 5 Hydroxyapatite50 50 40 7

<Evaluation of Adhesion Preventing Materials>

The adhesion preventing materials manufactured in Examples 11-17 weremade into a film having a thickness of about 100 μm using a hot pressand sterilized with ethylene oxide. A part (5×5 cm) of an intestinaltract of a dog (body weight: about 10 kg) was detached and the adhesionpreventing material was fixed to the detached part by means of suture.Incisions were carried out after 4 weeks and 8 weeks and checkingwhether the detached part was adhered was carried out by naked eye and,as a result, in any of the adhesion preventing materials, the operatedpart was not adhered and repair of the tissue was noted.

Comparative Example 5

A binary copolymer of lactic acid with glycolic acid (70:30) having anumber-average molecular weight of 100,000 was synthesized by the samemethod as in Example 11. This was heated and kneaded at 200° C for 10minutes with tricalcium α-phosphate being sintered at 800° C. and havingan average particle size of 1 Am in a ratio of 70/30 by weight whereupona complex was synthesized. The resulting complex was made into a filmhaving a thickness of about 100 μm using a hot press but, since it had ahigh rigidity and was fragile, it was broken upon the stage of suture.

Comparative Example 6

A binary copolymer of lactic acid with ε-caprolactone (70:30) having anumber-molecular weight of 110,000 was synthesized in the same way as inComparative Example 5 and a complex was synthesized by the same methodas in Comparative Example 5. The complex was evaluated according to theevaluating method as mentioned in the above <Evaluation of AdhesionPreventing Materials> and, when an observation was done by means of anincision after 8 weeks, the degradation rate of the complex was slowinhibiting the repair of the tissue.

EFFECT OF THE INVENTION

The biomaterial prepared by the present invention comprising calciumphosphate and a copolymer of lactic acid, glycolic acid andε-caprolactone shows an excellent biocompatibility, appropriate strengthand degradation rate and is a material which is effective for theregeneration of tissues. When the biomaterial is used as areconstructing material for hard tissues or soft tissues, its strengthis retained during the period until the tissues are regenerated and itis absorbed into the organism together with the regeneration of thetissues whereby it does not inhibit the regeneration of the tissues. Inaddition, there is no foreign body reaction by the residue.

Further, the biomaterial for inducing the osteoanagenesis whereperiosteum is attached to a complex containing calcium phosphate and acopolymer of lactic acid, glycolic acid and ε-caprolactone prepared bythe present invention has an excellent biocompatibility, appropriaterigidity and degradation rate and can be freely adjusted depending uponthe shape of the site to be treated. The said complex is graduallydegraded in vivo whereupon calcium phosphate is released therefrom.During the osteoanagenetic stage, the material functions as a partitionbetween the site to be treated and the outer area, inhibits the invasionof fibroblasts from the surrounding soft tissues and forms anenvironment which is advantageous for the osteoanagenesis. At the sametime, hematopoietic cells are provided from the periosteum while calciumphosphate is provided from the said complex to promote theosteoanagenesis and, after the osteoanagenesis, the material ismetabolized or becomes a part of the bone in vivo. Accordingly, thematerial can be used for the therapy of big bone defect part for which acomplete therapy has not been possible in the conventional methods andthe material can be effectively used for a regenerative therapy of bonetissues.

Furthermore, the biomaterial for the prevention of adhesion inaccordance with the present invention is in such a structure thatcalcium phosphate is coordinated to a carbonyl group in the copolymer oflactic acid, glycolic acid and ε-caprolactone and, therefore, the acidwhich is produced as a result of degradation of the copolymer isneutralized by a degradation of calcium phosphate in vivo whereby thestrength of the material can be retained. Accordingly, the biomaterialshows a neutral characteristic in vivo and, therefore, damage of thebiotissues is very little. In addition, the biomaterial shows a veryhigh strength and, therefore, it is suitable as a material for theprevention of adhesion.

For example, when the copolymer used in the present invention having afilm thickness of 300 μm is solely dipped in a physiological saline of37° C. for 4 weeks, pH of the solution is 3-4 while, in the case of thematerial for the prevention of adhesion in accordance with the presentinvention, a neutral pH of 6.5-7 is retained. Further, with regard toits tensile strength, the necessary strength lowers within 2 weeks inthe former case of the copolymer only while, in the material of thepresent invention, its strength can be retained for 12 weeks or evenlonger.

Accordingly, the material for the prevention of adhesion in accordancewith the present invention does not inhibit the repair of the biotissuesand has a degradation rate which is suitable for the adhesion of theapplied site.

Although the shape of biotissues are complicated in general, it ispossible to manufacture various types of materials ranging from flexibleto highly strong ones by adjusting the composition and the molecularweight of the copolymer of lactic acid, glycolic acid andε-caprolactone. Therefore, the material of the present invention for theprevention of adhesion is not broken by compression of the tissues andcan be fixed to the tissues in a closely contact manner achieving anexcellent effect of prevention of adhesion.

Thus, when the biomaterial of the present invention for the preventionof adhesion is used in vivo, its strength is retained during the perioduntil the tissues are repaired and it is gradually absorbed into theorganism together with the repair of the tissues whereby it is amaterial for the prevention of adhesion which is applicable to a broadsite.

The biomaterial of the present invention for the prevention of adhesionshows an excellent biocompatibility and has appropriate strength anddegradation rate and, therefore, it has an excellent tissue repairingability. During the period until the tissue is repaired, its shape andstrength are retained and it is absorbed into an organism together withthe repair of the tissue whereby it is an excellent material where thetissues do not adhere to each other and there is no residue which causesthe foreign body reaction.

What is claimed is:
 1. A biomaterial comprising calcium phosphate and acopolymer of lactic acid, glycolic acid and ε-caprolactone, wherein theε-caprolactone content in the copolymer is within a range of about 1 toabut 45 molar % and the glycolic acid content in the copolymer is withina range of about 5 to about 70 molar %.
 2. The biomaterial according toclaim 1, which is a biomaterial for the induction of osteoanagenesis ora biomaterial for the prevention of adhesion.
 3. A biomaterial for theinduction of osteoanagenesis, characterized in that a periosteum isattached to the biomaterial comprising calcium phosphate and a copolymerof lactic acid, glycolic acid and ε-caprolactone.
 4. The biomaterial forthe induction of osteoanagenesis according to claim 3, characterized inthat a periosteum is attached by means of a suture and an adhesion tothe biomaterial.
 5. The biomaterial for the induction of osteoanagenesisaccording to claim 3, whose rigidity is 200-20000 MPa at 4-40° C.
 6. Thebiomaterial for the induction of osteoanagenesis according to claim 3,characterized in that the copolymer has a molar ratio of lactic acid,glycolic acid and ε-caprolactone within a range of 5-90:3-75:5-40 in thebiomaterial.
 7. A biomaterial for the prevention of adhesion comprisingcalcium phosphate and a copolymer of lactic acid, glycolic acid andε-caprolactone where the molar ratio of lactic acid, glycolic acid andε-caprolactone is within a range of 5-90:3-75:5-40.
 8. The biomaterialaccording to claim 1, wherein a ratio of calcium phosphate to thecopolymer in terms of weight is 1:0.1˜2.0.
 9. The biomaterial accordingto claim 1, which is manufactured by heating and kneading calciumphosphate with the copolymer.
 10. The biomaterial according to claim 9,wherein the heating/kneading temperature is 50-250° C.
 11. Thebiomaterial according to claim 1, wherein the number-average molecularweight of the copolymer is 30,000-200,000.
 12. The biomaterial accordingto claim 1, wherein calcium phosphate is tricalcium phosphate.
 13. Thebiomaterial according to claim 12, wherein tricalcium phosphate has aparticle size of 0.1 to 200 μm.
 14. The biomaterial according to claim12, wherein tricalcium phosphate is sintered at 650-1500° C.